If you dont take care of your batteries then they are doomed for failure. These Lithium-Ion batteries need "Delicate" care. It only takes one bad experience to ruin your battery and cause it to do potential damage in the future... example- rupture, fire, etc.
The MAJORITY of failures are because of improper care. I know many people did not receive instructions on how to care for the batteries or some did but just neglected to read them. If you take care of the batteries then they will last MUCH longer!
The main things are
-don't store in HOT places.
- dont leave sitting on a charger more then 24 hours. The best thing is to unplug the battery from the charge as soon as it is finished receiving its full charge.
- do not run the battery dead. When the light indicator on the back of the light turns red then turn it off! (dont wait for it to turn off on its own!)
- dont use chargers that offer "fast charges"
- running 2 headlights using a Y-cable is a bad idea. It will overwork the battery. Running a Headlight with the MS Taillight is ok since the tail light uses very little of the battery.
Here is a link to BATTERY CARE-
Take these instructions to heart and your batteries will last much longer and also will be SAFER!